This new grant application, which is based on a 35-year longitudinal study (T1-T7) of substance use, proposes to identify the determinants and barriers to health care services utilization in the fifth decade of life by charting the longitudinal pathways to the utilization of services by adults in early midlife (Aim 1). In addition, the proposed research will assess the long-term consequences of substance use (alcohol, marijuana, and tobacco) in this understudied developmental period (Aim 2). At T8, we will gather information about important areas of physical and psychosocial functioning in adults in early midlife (physical diseases, psychiatric disorders, and functioning in adult roles), and relate these to the histories of substance use. Extensive longitudinal data are available on the participants from previous waves of data collection, including adolescence (T2, T3), emerging adulthood (T4), and young adulthood (T5, T6, and T7). At T8, face-to-face interviews will be conducted with the participants. Psychometrically sound scales will be developed from the surveys. The primary data-analytic techniques will be structural equation modeling, growth mixture modeling and regression. This research will enable us to provide crucial information about factors facilitating and barriers impeding the utilization of health care services among adults transitioning to midlife. In addition the proposed research will provide insight into the cumulative impact of prolonged substance use on psychosocial and physical functioning in adulthood. Since substance abuse and dependence are chronic, relapsing diseases, which may persist throughout a person's life, studying their patterns and concomitants prospectively over the life course is of crucial importance to public health. PUBLIC HEALTH RELEVANCE: The significance of the proposed study lies in its potential to a) identify pathways to the utilization of health care services in adults transitioning to midlife, and b) to determine the association between developmental trajectories of substance use from adolescence to early midlife and physical, psychological, and social functioning in the fifth decade of life. Knowledge to be gained from this research is crucial for understanding supportive factors and barriers to health care service utilization. Studying the patterns and concomitants of substance use prospectively over the life course is also of vital importance to public health and will provide information for the development of interventions which serve the needs of adults in early midlife. Preventing and reducing substance use is an important mission of the National Institute on Drug Abuse.